Isolation of Microfibrils from Rat Vibrissal Follicles

The fibrillar nature of wool keratin is well established but considerable doubt still exists concerning the mode of aggregation of the constituent protein molecules . Early workers (7, 10, 12, 22) showed that it is possible to examine the contents of cortical cells of suitably treated wool samples with the electron microscope, and that (macro)fibrils, which can be discerned in the optical microscope (10), consist of smaller filaments with diameter ranging from 500 nm down to about 10 nm . Farrant et al. (7) considered the microfibril to consist of globular keratin molecules (10 nm in diameter) but it was pointed out by Jeffrey et al . (12) that "sufficiently drastic treatments (of wool) are effective in producing a globular appearance in the microfibrils" and they observed that the more complete isolation of microfibrillar material required extreme breakdown of both hydrogen bonds and disulphide cross-linkages . However, with the advent of ultramicrotomy and the application of electron stains such as osmium tetroxide (1, 19), thin cross-sections of wool revealed the typical filament-matrix texture, which consists of microfibrils, 7-8 nm in diameter, embedded in an osmiophilic matrix (19) . High resolution micrographs show microfibrils to possess a fine structure which Filshie and Rogers